1. Field of the Invention
The present invention relates to a liquid crystal display device and, more specifically, to improvements of a lateral electric field type liquid crystal display device in which electrification caused by static electricity and the like affects the display quality.
2. Description of the Related Art
In a liquid crystal display device of lateral electric field type such as IPS (In Plane Switching), there is a phenomenon where the black screen becomes whitish and the display quality is deteriorated when a liquid crystal panel is electrified by static electricity and the like. In order to avoid it, employed is a structure which prevents electrification of the liquid crystal panel, with which: a transparent conductive film such as an ITO (Indium Tin Oxide) film is provided on a display surface side of a color filter substrate (referred to as a CF glass substrate or a counter substrate hereinafter) of the liquid crystal panel; and it is connected to the ground from a front frame through providing a spring-type piece conductor made of metal such as a finger from the ITO film to the front frame.
However, due to reduction in the size of the frame, recently, it is becoming difficult to secure a sufficient area for the ITO film exposed part of the liquid crystal panel. Considering the tolerance for pasting the polarization plate, it is becoming necessary to attach the conductor such as the finger with the ITO film exposed part of about 1.0 mm width.
Further, considering the position precision of the finger and the like, it is becoming turned into a state where the ITO film of the liquid crystal panel cannot be connected securely from the front frame to the ground through the finger.
As described above, techniques for preventing electrification through earthing the liquid crystal panel are disclosed in Japanese Unexamined Patent Publication 2007-093716 (Patent Document 1) and Japanese Unexamined Patent Publication 2011-164529 (Patent Document 2). In the invention disclosed in Patent Document 1, a conductive tape is pasted on a conductive polarization plate to increase an area where the finger can be in contact. However, the conductive tape is extended to the display surface side and covers at least a part of the outer circumference part of a display surface, and that part becomes the substantial frame part. Thus, it is not suited for narrowing the frame.
Further, as shown in FIG. 10, Patent Document 2 presents a method with which: a conductive gum CG is stretched from an ITO film of a liquid crystal panel LCP towards the frame direction; and the conductive gum CG is sandwiched between a front frame UFR and a mold frame MFR along with top and bottom conductive sheets CT2 and CT1 to be electrically connected to the conductive sheet CT1 stably.
With the invention disclosed in Patent Document 2, the frame can be narrowed. However, there is no specific reference made regarding the connection state between the conductive gum CG and the ITO film of the liquid crystal panel LCP.
Further, the conductive gum CG of the invention disclosed in Patent Document 2 is fixed in a pressed state by being clamped via the conductive sheets CT1 and CT2 from the top frame UFR and the mold frame MFR. When there is a move generated in the liquid crystal panel LCP by oscillation or an impact and if the conductive gum CG is expanded/contracted to absorb the move of the liquid crystal panel LCP, it is assumed to have deterioration in the material of the conductive gum CG caused by expansion/contraction or bending. Provided that the conductive gum CG is not easily expanded/contracted or bent, exfoliation may occur in the contact part (stuck part) between the other end of the conductive gum CG that cannot be pressurized by clamping and the liquid crystal panel LCP due to the fact that the conductive gum CG is easily exfoliated from the liquid crystal panel LCP (see the second to fourth lines in paragraph 0038 of Patent Document 2). Therefore, it can be said that there is a limit in stably earthing the ITO film anyhow.
As described, the part where the ITO film is exposed from the polarization plate has become narrowed in accordance with the narrowed frame of the liquid crystal display device. Thus, with the narrowed exposed part of the ITO film, it has become difficult for the contact member such as the finger to contact with the ITO film with high precision and earth the ITO film.
It is therefore an exemplary object of the present invention to provide a liquid crystal display device of a fine display quality through achieving a narrowed frame and stably earthing a transparent conductive film such as an ITO film of a display panel to a front frame.